The molecular biology of standard vesicular stomatitis virus (VSV) and its defective inferfering (DI) particles will be studied. Their genomes and other virus-specific RNAs will be dissected by oligonucleotide finger-print analysis. These oligonucleotides will be ordered on the genome. With such a catalogue, the genomes of DI particles will be precisely mapped. Oligonucleotides shown to be at the termini or at other control regions of the RNAs will be sequenced. Such sequence information will be related to the ability of DI particles to interfere with the growth of the standard VSV as well as to compete with each other. Also, the sequence information will be related to specific binding sites, it any, for the VSV structural proteins L, NS, N and M. A search will be made for cells which will provide host function(s) having a differential effect on VSV RNA replication, on the generation of DI particle genomes, and on the degree of interference exerted by DI particles. Should such systems be found and characterized, attempts will be made to isolate and identify the host components necessary for VSV RNA synthesis.